It will be understood that because of the tremendous impact forces acting upon the grate assembly by virtue of the high speed rotation of the hammers as they reduce, by shear crushing, etc. metallic materials such as auto bodies, small motors, ores, slags, solid wastes, and the like, there is a great need for an extremely efficient means for obtaining rapid access and entry to both the grate system and the hammers of the hammer mill to replace worn parts, or to reverse certain grate components to present fresh shearing surfaces--all for the purpose of maintaining, as closely as possible, the optimum dimensional relationship between hammers and grate assembly, with minimum down-time, for a wide variety of materials ranging from municipal wastes to fractional horsepower motors.
The grate assembly system of my previous invention patented in U.S. Pat. No. 4,226,375 issued on Oct. 7, 1980 and entitled "Reduction Mill" incorporates therewith a series of spaced cutter bars, these cutter bars coacting with rotating hammers of the hammer mill section to effect size reduction by shear, as well as by crushing or pulverizing of the material entering the mill charging area. The entire grate assembly system is concentrated within an approximately 140.degree.-170.degree. arc mounted in the side of the reduction mill, i.e., over an arc extending from approximately 6:30 to 11:30 o'clock. The entire grate assembly system is mounted within a grate housing that is pivotally mounted so as to be readily disengaged from, and re-engageable with, the mill cage housing or zone. Pivotal disengagement and re-engagement of the grate housing is optimally made under power means, such as an hydraulic ram or piston.
There are major advantages to the mode of assembly of grate components described in my aforesaid U.S. Pat. No. 4,226,375. First, the concentration of all grate components over a 6:30 to 11:30 o'clock arc of 140.degree.-170.degree. in combination with the entire pivotal disengagement thereof enables every component of the grate system to be readily accessible for reversibility or replacement. It also permits the hammers of the rotary hammer mill to be readily accessible for inspection and/or replacement. Ready accessibility enables predetermined tolerances to be more readily attained. The side discharge permits the entire bottom of the mill to be a solid anvil wall and to be placed upon on-grade foundations rather than requiring foundations to be dug below grade in pits or the like--as is the case in bottom discharge mills.
Rotary hammer mills generate tremendous impact forces on the material to be comminuted by virtue of the high speed rotation of the hammers. Occasionally an oversize piece of uncrushable material is inadvertently fed to the reduction mill. If the reduction mill is not quickly stopped and/or the uncrushable material rapidly removed, internal damage to the hammer mill portion, or to other portions of the reduction mill may occur. The oversize piece may even be caused to ricochet and be ejected rearwardly from the entrance to the reduction mill, and become a severe, perhaps even fatal safety hazard to human beings working in the vicinity of the reduction mill.
Pivotal displacement of by-pass doors, permitting removal of uncrushable materials from a reduction mill of the type employing rotary hammer mills, are known in the art. The following prior art offers various solutions to the problem of removal of uncrushable materials:
______________________________________ PATENTEE U.S. PAT. NO. ISSUED ______________________________________ Liggett 1,625,554 4/19/27 Konig et al. 4,049,206 9/20/77 Whitney 4,146,184 3/27/79 ______________________________________ Recycling Today, Page 138, July 1980
Liggett's grate system is formed in two parts, one part fixed, and one part displaceable. The displaceable portion of the grate system is pivotally displaceable to permit escape of uncrushables. No means is provided in Liggett for providing ready access to the entire grate system (because one portion is fixed) for replacement, repair, etc. The Liggett reduction mill, while permitting uncrushables to exit from the mill, by means of an opening provided by a pivotally displaceable portion of the grate system, intermingles oversize uncrushables with the sized product stream thus resulting in an inferior product--since the product is usually sold on the basis of size of comminuted product.
Konig's trash comminuter permits removal of uncrushables by displacement of the grate system components from the rotor portion of the reduction mill by two separately powered units and operations. Fine comminution of material must be discontinued until the uncrushables are removed because the grate system itself is displaced in order to remove the uncrushables. The oversize uncrushables enter the product stream.
Whitney, U.S. Pat. No. 4,146,184, also has a pivotally displaceable door, containing grate components. Displacement of the door, to permit removal of uncrushables, necessarily results in intermingling of the oversize uncrushable material with the product stream.
The July 1980 Recycling Today publication describes a scrap shredder having a by-pass door which does not contain any grate components. The by-pass door may be pivotally displaced to permit removal of oversize uncrushable materials. The uncrushables intermingle with the product stream as in Whitney, Liggett and Konig.
These aforementioned patents and publication represent the closest prior art known to the invention described and claimed herein.